AA is an inherent side product which is generated during the polymerization melt phase and subsequent processing of PET and other polyesters into useful articles such as containers. Some amount of residual AA may remain in the finished articles. The amount of residual AA level depends in part on the conditions used to process. For example, poly(ethylene terephthalate) (PET) resin prepared using dimethyl terephthalate (DMT) leads to typically 9-10 ppm AA in the bottle sidewall; however, terephthalic acid (TPA) based PET resins lead to much lower levels of AA in the bottle sidewall, i.e., 5-6 ppm. Despite the significant improvement in the TPA based resins, this level of AA is still perceived to be too high. In fact, customer taste testing has indicated that consumers can taste about 20 ppb differences in AA. Consequently, there has been significant customer interest in reducing the residual AA content as low as possible.
Because water contains various contaminants it is desirably disinfected prior to bottling. Chlorination and ozonation are two common methods for disinfecting spring water. The ozonation process leaves residual ozone in the water which is subsequently bottled. Ozonated water stored in conventional PET containers may acquire an undesirable taste due to the presence of various flavorants such acetaldehyde and/or other compounds, some of which may be the byproduct of the ozonation process. Thus, it is highly desirable to provide containers for use with ozonated water that have acceptable flavor retaining properties and clarity.
U.S. Pat. No. 5,258,233 discloses the use of a blend of a low molecular weight polyamide with PET to reduce acetaldehyde. In this patent, it is stated that less than 2% polyamide should be used to minimize color and haze. Similarly, U.S. Pat. No. 5,266,233 discloses the use of a blend with low molecular weight polyamide with PET copolyesters to reduce acetaldehyde. U.S. Pat. No. 5,340,884 discloses the art of precompounding the polyamide with polyesters to create a concentrate that can be diluted with a polyester and still yield the desired properties.
Jammes et al describe the formation and behavior of some keto acids and aldehydes in drinking water treatment process including an ozonation step (Fr. Rev. Sci. Eau (1995), 8(3), 333-54). Specific disinfection byproducts may also induce immediate water quality deterioration due to the objectionable organoleptic properties. Anderson et al describe in Can. Proc. Water Qual. Technol. Conf. (1994), Pt. 1, 871-908 the ozone byproduct formation in three different types of surface waters. Ozonation byproducts which were examined in this study included: acetaldehyde, propanol, butanol, pentanol, hexanol, heptanol, octanol, benzaldehyde, glyoxal, and methyl-glyoxal, oxalic acid, pyruvic acid, oxalacetic acid, and similar organic compounds.
U.S. Pat. No. 5,362,784 disclosed compositions of polyalkylene imine (PAI). Particularly polyethylene imine (PEI) and polyester polymers, including copolymers and derivatives thereof; such compositions can be used in producing films and devices which are capable of scavenging unwanted aldehydes. However, there is no disclosure regarding the use of ozonated water in containers made from the resin blends.
J. Poly. Sci: Part A Polymer Chemistry, 34, 3573(1996) disclosed the use of N-dialkyl amides, particularly dimethyl acetamide as sacrificial ozone scavengers, in the preparation of functional polystyrene. The publication does not disclose the use of polyamides either separately or in combination with polyesters. In addition, there is no indication that the dialkyl amides improve the flavor of ozonated water packaged in polyester containers.
JP 92-317959 921104 discloses the use of ozone for the disinfection of water, typical process and concerns known in the industry. The patent does not describe the use of polyamides as a method to improve the taste of the ozonated water.
J. Dairy Sci. (1994), 74(1), 96-9 describes the describes the effect of ozone on the taste of water packaged in poly(ethylene) containers. The "off-taste" generated during ozonation could be controlled by the treatment of the containers with butylated hydroxytoluene (BHT, 185 ppm). The publication does not describe the "off-taste" in polyester containers, nor the use of polyamides to improve the flavor of the water.